Influence of metallicity on effective temperature of star

[Anne-Sylvie]

Hey everyone,

This is my first post on this forum. Please tell me if I do some mistake. :)

So, there is my question ; I have search a long time on the web but I don't find any answer...

Why the metallicity influences the effective temperature and the luminosity of a star ?

I read somewhere that the more metallic star, the more opaque the atmosphere. Because there are more transition lines available for photons to be absorbed or something like it.

But I don't see why this implies a change in luminosity or temperature.

Any idea ? Thanks a million ! :)

Have a nice day !

 

[QuArK21343]

I am really no expert but I guess that higher metallicity Z means comparatively more free electrons and so higher opacity - or less luminosity and effective temperature. Some mathematical details can be found at this link: http://www-star.st-and.ac.uk/~kw25/teaching/stars/STRUC11.pdf Hope it helps

 

[Anne-Sylvie]

Hello QuArK,

Thanks for your answer. The pdf link is interesting.
But I'm searching a more physical and intuitive answer... Why a higher opacity implies a lower effective temperature ?

Edit : I think I have got it !
http://www2.astro.psu.edu/users/rbc/a534/lec18.pdf
On the third page.

Thanks you ! :-)

 

[nicksauce]

Why a higher opacity implies a lower effective temperature ?

I mean, there's a very simple answer. Imagine you're perfectly transparent, so the opacity is zero. Then all the light escaping is the same light from the core, so the effective temperature if very high. Now imagine you're perfectly opaque, so that no light escapes at all. Then you're effective temperature is zero.

 

[Anne-Sylvie]

Indeed.
Thanks !